1. Field of the Invention
The present invention relates to a scale having two sets of numbers at exactly fixed distance apart for measuring things, and more particularly to a measuring instrument marked with a metric scale and a inch-and-foot scale for the sake of facilitating the conversion from one to the other. In the general tendency of transition to the metric system such a scale is useful in inducing workers who are still measuring things in terms of inches and feet in the architectual fields to get used to the metric system.
2. Prior Arts
Scales are widely used for measuring the lengths of different things not only in architectural works but also in homeworks. The scale is the most primitive one of all the tools used in architectural works.
A variety of scales such as a architect's scale, an engineer's scale or module are used. The word, "scale" used herein after should be understood as including every sort of scale actually used for measuring the lengths of things.
As is well known, different measuring systems are used in the world. For instance, in America and other countries things are measured in terms of inch and foot. This is especially so in building wooden houses and big buildings. There is, however, an active movement for world-wide standardization of linear measurement. In the TAG8 international standardization of linear measurement in architecture, the metric system is adopted as measure of length, one meter being equal to one hundred millimeters (1M=100 mm). Thus, it has been popular that scales marked with inches are additionally marked with centimeters. Such scales have two sets of marks parallel arranged with the proportion of 1 foot to 304.8 millimeters, and 1 inch to 25.4 millimeters in marking.
Thus, one can find the corresponding number of metric system from given number of feet or inches on the scale. This sort of scale, however, is designed in principle for linear measurement in terms of feet or inches, permiting conversion to the metric system only when occasions demand. Use of such scales makes for the continuous use of inches and feet in measuring things in architectural fields, making it difficult to use the metric system alone no matter how long a period workers may use and get used to such scales. As a matter of fact, it is very difficult to induce them to get used to the metric system so far as such scales are used; they are actually used as the inch-and-foot scale.
Also, when given lengths determined in terms of inch and foot are converted to corresponding metric measurement, required calculations must be effected by using a conversion rate, which is given decimally (for instance, with the aid of desk calculators). No matter how far the conversion rate may be decimally determined, the conversion rate itself contains more or less errors, and therefore, conversion into the metric system will ineviably cause some errors.
The above description is directed to conversion of inches or feet into centimeters and meters. This is also the case with "SUN" and "SHAKU", which are used as units in linear measurement in Japan. The inventor invented a scale facilitating conversion of "SUN" or "SHAKU" into the metric system, and filed a utility model application on Jul. 15, 1986 in Japan. The application was registered as Utility Model Registration No. 3,007,370.
The conversion rate is determined so that 1 "SHAKU" may be equal to 33+(1/3) centimeters for the purpose described later, and a set of marks are made on the basis of 1 "SHAKU" for every ten "SUN"s on the surface of long instrument. This is not correct from the mathematical point of view. Such apparent equality between the two different measuring systems, however, has the effect of putting selected marks in alignment in different measuring systems, giving still permissible approximation in conversion from the metric measurement to "SUN"- or "SHAKU". Workers realize that measurement based on centimeters and meters is correct, and therefore, they will be led to use of metric system when they get used to such scales.
As a matter of course such scales cannot be applied directly to conversion of inch or foot into centimeter or meter; the measuring system using "SUN" or "SHAKU" as units of length is totally different from the measuring system using inch or foot as units of length.